"The Tree Identification Book" by George W. D. Symonds
"The Pine Tree Book" by Russell Peterson
"Trees of North America" by C. Frank Brockman
"The Audubon Society Field Guide to North American Trees, Eastern Region" by Elbert L. Little
Peterson Field Guide: "Eastern Trees" by George Petrides and Janet Wehr
Falcon Guide: "The Easy Tree Guide -- Common Native and Cultivated Trees of the United States and Canada" by Keith Rushforth
"Botany Everywhere" by Martin Michener (a revolutionary electronic-format guidebook for New England plants)